When derivating an existing image with an existing entrypoint (think apache, mariadb, etc), it is quite common to have some extra process needed to be done at the entry point (aka wiring/glue things), but at this time there is no clean way to prepend operation before the entrypoint.
AFAIK, the current way would be to duplicate the entrypoint script and update it with your own required extra work. The issue with this is that as soon as the entrypoint of the parent image is updated, you can have a broken image. There are also solutions that the parent entrypoint script would provide some extra “extension script” as bundled. But it is almost never the case, and you can not spend your life trying to convince all the image maintainer to do so
I propose to get somethign like PRE_ENTRYPOINT_RUN.
The idea is that before calling the entrypoint, docker will build a list of PRE_ENTRYPOINT_RUN command and execute them in the parent to child and in the first to last order. Once done, it will do the usual job for ENTRYPOINT.
Doing so, you would be able to derive a existing container including its entrypoint but bring extra glue on it for your extra features of your image without impacting the parent image.
The name of the command PRE_ENTRYPOINT_RUN can be changed … but I think the name is quite clear.